The mechanical testing effort at the Hospital for Special Surgery needs to adapt its focus, reach out and expand collaborative relations, and respond to the needs of a new user base. HSS investigators have pioneered bone mechanical testing and performed many fundamental characterizing bone material properties from a purely mechanical perspective. Advances in molecular biology and genetics now allow identification of local and systemic factors that can affect skeletal integrity, so that the emphasis can become more integrated between "biological" and "engineering" experiments. Therefore, the goal of the Mechanical Testing Core is to organize and enhance the testing facility at HSS by providing testing equipment and methodologies for material and structural characterization of bone, by training investigators in the use and interpretation of material and structural testing, and by developing new applications and methodologies to fit the research programs of investigators within the Core Center's biomedical research base. New testing approaches suitable to the biological approaches being used in current and planned experiments described elsewhere in the Core Center proposals are being developed, particularly for in vivo small animal experiments. These efforts were begun as part of a "small animal testing" user groups, consisting of bioengineers, clinicians, biologists, chemists, and their students, that has been active for the past year (and which was the initiation point for the Core Center proposal). The changes required to organize and refocus the mechanical testing effort can be made within the existing infrastructure, using well-established techniques developed at HSS.